1. Field of the Invention
The present invention relates to a composite selector fork arrangement, a composite selector fork arrangement when mounted on a selector rod, a method of mounting a composite selector fork, a method of forming a composite selector fork, a method of forming a composite selector fork arrangement, a selector rod and a selector fork arrangement and a mounting arrangement for a first and second member.
2. Discussion of Related Art
The manual transmission of motor vehicles involves the axial movement of a shift fork in order to operate a sliding synchroniser sleeve or clutch. The shift fork is mounted on a shaft that is remote from the sliding clutch with the shaft also being movable axially upon operation of a gear shift mechanism. A considerable force is required in order to effect the movement of the shift fork when the shift shaft is moved to thereby cause the remote synchroniser sliding sleeve or clutch to move to cause a gear to be engaged or disengaged. Furthermore, the attachment of the fork to the shift shaft requires to be quite accurate in the axial direction in order to ensure correct engagement and disengagement of the gears upon the remote movement of a gear shift mechanism. In addition, the environment of the transmission is a harsh environment that is subject to high temperatures.
Accordingly, transmission shift forks have traditionally been made of metal. This has many disadvantages including the cost of construction that requires casting of the metal and then post machining of the metal by milling or drilling. In addition, in order to secure the fork to the shaft, the fork and the shaft have to be drilled, aligned, and pinned together. This makes assembly of the transmission shift forks into the transmission time consuming and expensive.
One such metal selector mechanism is shown in FIGS. 1-3 in which FIG. 1 is an axial view of the selector mechanism, FIG. 2 is a section taken along a line 2--2 of FIG. 1, and FIG. 3 is a section taken through the line 3--3 of FIG. 1.
A selector or shift fork 14 is cast out of metal and then machined to give the shape shown. The fork 14 is required to be connected to a circular selector shaft 2. As shown in FIGS. 1 and 2, the fork 14 extends partially around, and within a groove 10 formed in the circumferential extent of a sliding sleeve 11 whereby the fork and the sleeve are constrained to move together axially. The fork 14 is provided with circumferentially spaced pads 12a and 12b of plastics material that transfer forces between the fork 14 and the sleeve 11.
Axial movement of the sleeve 11 along a shaft (not shown) causes axially spaced gears either side the sleeve 11 to be engaged or disengaged with a drive in a conventional manner.
The fork 14 includes a hub 22 at its upper end having a cylindrical opening 23 that is located on a gear shift rod 2. A pin 18 is passed through the opening in the hub 22 and an opening in the shift rod 2 when those openings are aligned, in order to secure the rod and fork together.
The hub 22 may be directly formed with a lug 15b, which lug is used to transfer forces applied by a gear shift mechanism (not shown) to the selector fork in order to effect the required axial movement of the sleeve 11. In an alternative, instead of the lug 15b being provided directly on the hub 22, an axially spaced shift block 16 may be secured by a pin passing through that block 16 and the shaft 2 with that block 16 having a lug 15a. When forces are applied to the lug 15a, as shown at 19a, those forces are transferred through the block 16, the pin 18 and the shaft 2 to the selector fork 14 via the pin 18 that extends through the hub 22.
There can be problems in machining and assembling the mechanism shown in FIGS. 1 to 3 not only in terms of manufacturing difficulties but also in terms of ensuring that all of the parts are axially and radially aligned. In this respect it will be appreciated that a hole has to be drilled to the shift block 16 and also into the hub 22. Holes also have to be drilled through the shaft 2 (thereby weakening the shaft) with the parts then being assembled. Any inaccuracy between where all of those holes are drilled can result in incorrect axial alignment of the pads 12a and 12b with respect to the lugs 15a or 15b.
Furthermore, the pads 12a and 12b are preformed, and fit over the leg forming the T section similar to the one shown in FIG. 3 such that there is no possibility of any axial misalignment being able to be compensated for with the pads 12a and 12b.
Plastic selector forks have been proposed. However, the high performance plastics required is extremely expensive especially to cope with the high temperature differentials. Furthermore, although the plastics can have the strength necessary to effect the shift required without significant bending, the plastic has to be sufficiently large to withstand the bending forces resulting in increased volume and increased expense. As the size available within a transmission housing is generally restricted, it is not really practical to consider using such large pieces of plastics in such a confined space. Larger forks may also lead to further complications by shrouding the gear and synchroniser assemblies resulting in oil flow restrictions.